Th vasodilator, designated as the antihypertensive polar renomedullary lipid (APRL) (hypertension 1:299, 1979), was identified, during the year, as an alkyl ether of phosphotidylcholine. In position 1 was the alkyl ether, in position 2 an acetoyl and in position 3 phosphocholine. The most prominent chain length (approximately 60%) for the ether was Cl6:0. This glyceryl alkyl ether exerted an antihypertensive effect in hypertensive rats and rabbits when given by mouth. A proper dose schedule was effective for 40 hours after the last input of the compound without evidence of toxicity, including no change of platelet and leucocyte counts. The hypertension induced by JG-like cells, grown as monolayer tissue culture, appeared due to a very high plasma angiotensin level, during its development. After 30 days, the plasma angiotensin receded to baseline. Renomedullary interstitial cells (RIC) were not effective against this hypertension in the developmental phase but were so during the maintenance phase. This suggests that angiotensin impairs the antihypertensive action of RIC. In three hypertensive models, wherein the RIC were either absent or severely damaged, converting enzyme inhibitors (teprotide and captopril) were not antihypertensive. This suggests a relationship between the action of these compounds and the antihypertensive action of RIC, under these circumstances.